The aim of this program is to increase the basic understanding of how innate behavior patterns (i.e. "fixed action patterns") and recognition mechanisms (i.e. "innate releasing mechanisms") are coded in and controlled by the nervous system. For this purpose, anuran (toads and frogs) acoustic behavior, i.e. calling and responses to calls, is being studied. This behavior is especially appropriate because of its relative simplicity, the species-specificity of some calls, and the fact that some calls can be elicited in essentially normal forms by brain stimulation. Anurans are especially appropriate because of their high tolerance of radical surgical procedures, accessibility and simplicity of their nervous systems, and ready availability and maintenance. Much of the current work is based around an isolated brainstem preparation. In this technique, the brainstem of a frog is removed and placed in a tissue bath. Neural correlates of calling can be elicited then by electrical stimulation of the preoptic area. The development of such correlates is being studied in metamorphosing frogs. This preparation is also being used in anatomical studies involving the autoradiographic localization of tritiated compounds (e.g. 2-deoxyglucose, leucine, neurotransmitters, horseradish peroxidase) applied to the isolated brain.